Chemical-mechanical polishing generally involves pressing a substrate against a wetted, polishing platen within a polisher apparatus, with the conditions being controlled as to the temperature, pressure, and chemical environment. In a typical chemical-mechanical polishing ("CMP") apparatus, a pad is glued onto a circular metal platen in the polisher. The CMP pad is usually about twenty to thirty inches in diameter and 100 mils in thickness, depending on the application. The pads are customarily formed of a relatively soft material, such as polyurethane. The substrate to be planarized is placed on a carrier and then pressed against the pad while both the pad and substrate rotate, as a polishing slurry is applied. The polishing slurry often is comprised of abrasive materials (i.e., silica, alumina, or ceria), suspended in water, with additives to obtain a specific pH and create oxide layers on the materials to be polished that can be abraded easily by the particles. In some applications, such as those involving a silicon substrate or metal polishing, the friction between the substrate and the pad can generate a significant amount of heat.
For example, FIG. 1 illustrates a pad and platen as used in a typical CMP polisher apparatus. As shown in FIG. 1, a CMP apparatus comprises a pad 10 and a platen 12; a layer of adhesive 14 secures the pad to the platen when they are pressed together following the arrows A. The substrate 16 to be planarized is secured to a carrier 18. The carrier 18 may include a vacuum (not shown) for holding the substrate to the carrier during the load and unload steps. While polishing, however, the vacuum is normally deactivated, and the substrate 16 is held in place by the high coefficient of friction between the carrier 18 and the substrate 16. Also, the carrier may be conformed (e.g., with use of a polymer sheet or wax) to receive the substrate 16, and it may be adapted to receive a plurality of substrates to be planarized simultaneously. In operation, a polishing slurry 20 is placed over the pad 10, and the carrier 18 presses the substrate 16 against the pad following the arrow B. The carrier 18 and/or the platen 12 may rotate the substrate on the pad, or vibrate or oscillate, as illustrated by the arrows R. As the whetted pad 10 is pressed against and moved across the surface of the substrate 16, the surface of the substrate is polished by chemical and mechanical means, the aim being to remove metal layers or achieve a smooth and uniform surface.
This CMP process has become the process of choice for planarizing interlevel dielectric layers, particularly as circuit densities have increased. A major issue in planarizing the layers involves achieving a substrate surface that is completely smooth and uniform. Often, irregular or wavy surfaces may be formed on the substrate, occurring at the microlevel and having a negative impact on the productivity and reliability of the integrated-circuit devices. Much effort has been applied to developing improved CMP methods for efficiently obtaining a uniform planarized surface. Efforts have been made, for example, to develop new materials and apparatuses for the parts that are directly adjacent to or impact upon the substrate surface, that is, the carrier, the slurry, the pad, or the substrate itself. See, for example, U.S. Pat. No. 5,643,053, to Shendon issued Jul. 1, 1997, entitled "Chemical Mechanical Apparatus with Improved Polishing Control" (addressing the carrier); U.S. Pat. No. 5,609,719, to Hempel issued Mar. 11, 1997, entitled "Method for Performing Chemical Mechanical Polish (CMP) of a Wafer" (addressing the pad and its ability to retain slurry); U.S. Pat. No. 5,514,245 to Doan et al., issued May 7, 1996, entitled "Method for Chemical Planarization of A Semiconductor Wafer to Provide A Planar Surface Free of Microscratches" (addressing the pad composition); and U.S. Pat. No. 5,449,314 to Meikle et al., entitled "Method of Chimical [sic] Mechanical Polishing for Dielectric Layers" (addressing the composition of the substrate itself).
The instant invention provides an improved apparatus and method in which difficulties with the CMP process are addressed through parts that are not directly adjacent to the substrate surface. Further advantages of this invention should appear more fully upon consideration of the detailed description given below.